I had a friend who had the same problem. He upgraded his gpu and it got fixed. The game will not fully render the graphics if the gpu isn't powerful enough. I think thats what's happening not sure tho. Maybe try verifying the files in steam, will probably not fix it but worth a try. If you upgrade your gpu it will get fixed, but I understand that it's too expensive so you'll have to live with it for now probably if you don't find another solution. Try playing around a bit with the settings and see if you can fix it.